1. Field of the Invention
The invention relates a process for the preparation of substituted aromatic carboxylic acid esters. In particular the invention relates a process for the preparation of nitro-substituted aromatic carboxylic acid esters and thioether-substituted aromatic carboxylic acid esters. Such aryl esters are useful intermediates in the preparation of agrochemicals and agrochemical intermediates.
2. Description of the Related Art
Aryl 1,3-diketones are important synthetic intermediates for a variety of industrially-produced chemicals, such as herbicidal isoxazole derivatives. For example, EP 470856 describes various herbicidal isoxazole derivatives and a process for their preparation from aryl 1,3-diketones. WO 97/28122 describes the preparation of 1-aryl-3-cyclopropyl-1,3-diketones as intermediates used to prepare agrochemicals (e.g. herbicides, pesticides). These 1,3-diketones can be prepared by reacting a substituted acetophenone with a cyclopropanecarboxylic acid ester. However, in addition to the difficulty of preparing the starting substituted acetophenone, the reaction only affords a moderate yield of the desired 1,3-diketone. Aryl 1,3-diketones can also be prepared, as described in WO 95/00476, by hydrolysis of β-aminovinyl ketones resulting from the reaction between a ketone and a substituted benzonitrile. WO 95/00476 also discloses that reacting a ketone with a substituted benzoic acid ester (prepared from the hydrolysis and subsequent esterification of an aromatic nitrite) also leads to the formation of aryl 1,3-diketones.
Preparation of benzoate esters by the metal-catalyzed carbonylation of an unsubstituted aryl halide substrate, especially an aryl iodide substrate, in alcohol is a well-known process. See, e.g. Schoenberg et al, J. Org. Chem., 39, 3318 (1974); Stille and Wong, J. Org. Chem., 40, 532 (1975); Takeuchi et al, J. Chem. Soc., Chem. Commun., 351 (1986); Hicai et al, Bull. Chem. Soc. Jpn, 48, 2075 (1975); Ito et al, Bull. Chem. Soc. Jpn., 48, 2091 (1975); Takahashi et al, Chem. Lett., 369 (1980). While aryl bromide substrates are moderately active in such reactions, aryl chlorides are generally inert, although limited success has been achieved with aryl chloride substrates using customized catalysts.
Metal-catalyzed reductive carbonylation of nitroaromatic compounds in alcohol is also a well-known process. Sundermann, R., et al., Appl. Homogeneous Catal. Organomet. Compd., 2, 1072-1080 (1996). Under such reaction conditions reduction of the nitro group results affording aniline derivatives or related compounds. For example, the reaction of nitroarenes with carbon monoxide in alcohols with catalytic rhodium complexes results in the formation of urethanes. Id. Accordingly, since the nitro group is prone to reduction, the metal-catalyzed carbonylation of aromatic substrates substituted with both a halo and a nitro group in alcohols is generally avoided.
Thus there still exists a need in the art for a method of preparing nitro-substituted aromatic carboxylic acid esters from nitro-substituted aryl halide substrates under metal-catalyzed carbonylation reaction conditions without reduction of the nitro group. Such compounds are useful precursors for the preparation of 1,3-diketone agrochemical intermediates.